(1) Technical Field
The present invention relates to a five-membered heterocyclic compound polymer having a novel structure which is useful for electronic materials and display material and the preparation thereof.
(2) Background Information
There have been proposed a process for producing a polymer composition by the electrolytic oxidation of pyrrole in the presence of a supporting electrolyte such as tetraethylammonium tetrafluoroborate (for example, Keiji Kanazawa et al., J. Chem. Soc. Chem. Comm. 854 [1979]) and a process for producing a polymer composition by the electrolytic oxidation of thiophene in the presence of a supporting electrolyte such as tetraethylammonium tetrafluoroborate (for example, Robert J. Waltman et al., J. Phys. Chem. 87, 1459 [1983]).
These compositions have high electric conductivity and are useful for electric conductive materials. Japanese Provisional Patent Publication No. 59-129827/1984 discloses that these compositions are useful also for display materials, because the light transmission spectra are clearly varied depending on whether the compositions are in the doped state or in the neutral state (namely, wherein the dopant is removed) due to their electrochemical responsiveness. Further, Japanese Provisional Patent Publication No. 58-196233/1983 discloses a process for producing a polymer composition by the electrolytic oxidation of 2,2'-thienylpyrrole or 2-(2-pyrrolyl)thiophene as a raw material.
Polypyrrole (pyrrole polymer composition) has, however, a reduction potential of -0.3V, which is more negative than that of the oxygen molecule which is -0.2V. Consequently, the stability of polypyrrole in the neutral state in the air is not good, because polypyrrole is oxidized by oxygen. Polythiophene (thiophene polymer composition) has an oxidation potential of about 1.0V, which is near to that of water molecule which is +1.2V. As a result, polythiophene is easily reduced by moisture in the air. It is, therefore, difficult to maintain the high electric conductivity in the air, resulting in difficulty for its practical use.
Also, with respect to their use for display materials, the instability described above causes a low cycle life of only about 10.sup.6 cycles, whereas the level required for practical use is more than 10.sup.7 cycles. In the present situation, therefore, it is difficult to use them in practice.
The polymer composition obtained by the electrolytic oxidation of 2,2'-thienylpyrrole or 2-(2-pyrrolyl) thiophene contains perchlorate ions as the dopant, because magnesium perchlorate is employed therein as a supporting electrolyte. Nevertheless, this polymer composition shows only a low electric conductivity of 2.6.times.10.sup.-1 (.OMEGA..multidot.cm).sup.-1, compared with that of polypyrrole and polythiophene which contain the perchlorate ions. This phenomenon is considered to result from such a structural defect of this polymer composition as the bond at the 3- and 4- positions, not at the 2- and 5- positions, compared with polypyrrole or polythiophene (Japanese Provisional Patent Publication Nos. 58-187432/1983, 58-196232/1983, 58-213027/1983, 59-51918/1984, 59-191727/1984, 59-207931/1984, 59-207932/1984 and 59-210947/1984).